You will find the Carpe Diem kombucha in every major supermarket here in Austria. This kombucha is marketed by a company owned by the same Dietrich Mateschitz who is a billionaire from selling Red Bull worldwide ...

I'm highly amused that their website shows a man in Japanese garb and Japanese writing on a rock, and yet if you went to Japan and asked for "kombucha" you'd get quite a different beverage from these concoctions -- a thin salty tea (cha) made from kelp (kombu). I'm curious how that name came to be applied to this stuff.

While in Japan konbucha is a konbu kelp drink and not made from the tea leaf, it is a very valid name to call the fermented tea drink kombucha as kombucha because that is its name--even if in Japan this black tea drink is called a koucha (black tea) kinoko ("child of a tree" or mushroom) drink. And it's a readily available tea in Japan so it's not strange to use Japanese themes in the marketing. Kombucha is the name this fermented tea was known by long before Carpe Diem marketed its beverage. The bacterial culture used to ferment the tea is known as a kombu culture. In Japan it's referred to as a "mushroom" because the fermenting yeast/bacteria colony's resemblence to the cap of a mushroom like the shiitake. But I've heard it said the "kombu" name refers to a Chinese leader who was once treated using the healthful properties of this bacterial strain. Sounds like mythmaking to me to be sure, but it's certainly no modern convention nor error to call the Carpe Diem beverage kombucha.